Leather tanning agent and process for making same

ABSTRACT

A leather tanning agent characterized in that it contains the following components, percent by weight: 
     
         ______________________________________                                    
 
    
     sulphate of aluminum and ammonium                                         
                         3 to 20                                          
containing 0.001 to 1.0% of TiO 2  or                                  
TiO 2  and ZrO 2                                                    
and/or sulphate of zirconium and ammonium                                 
                        20 to 50                                          
containing 0.001 to 0.5% of TiO 2                                      
or TiO 2  and Al 2  O 3                                          
and sulphate of titanyl and ammonium                                      
containing of 0.001 to 1.0% of Al 2  O 3                            
and/or ZrO 2         the balance.                                      
______________________________________                                    
 
     The above-mentioned additives of TiO 2 , ZrO 2  and Al 2  O 3  incorporated in the sulphates are present therein in a chemically combined state. 
     In the process for producing the leather tanning agent a titanium-containing solution with a concentration of titanium of from 80 to 200 g/l as calculated for titanium dioxide is reacted with a solution of aluminum sulphate containing 80 to 130 g/l of aluminum as calculated for alumina, and/or a solution of zirconium sulphate containing 50 to 200 g/l of zirconium as calculated for zirconium dioxide in the presence of sulphuric acid and ammonium sulphate. 
     The sulphate tanning agent according to the present invention can be very useful in the leather industry.

FIELD OF THE ART

The present invention relates to the leather industry and, morespecifically, to a leather tanning agent and to a process for makingsame.

The prior art tanning agents employed in the leather industry includechrome tanning agents and vegetable tanning agents comprising extractsof oak, spruce, willow, chestnut, quebracho, mimosa, and the like. Theuse of chromium is harmful for operating personnel, and causesenvironmental pollution. The use of vegetable tanning agents requiresconsiderable amounts of vegetable raw materials, thus, also renderingdamage to the environment.

DESCRIPTION OF THE PRIOR ART

Known in the art is a titanium tanning agent for hides comprising adouble sulphate of titanyl and ammonium in the monohydrate form (NH₄)₂TiO(SO₄)₂.H₂ O (cf. USSR Inventor's Certificate No. 234598, Cl. 28apublished in 1969). The use of titanium tanning agent eliminates thenecessity of using vegetable tanning agents and considerably reduces therate of consumption of chrome tanning agents. Titanium tanning agentsmake it possible to efficiently carry out the process of tanning hides.The hides acquire improved characteristics, but the temperature oftanned pelt shrinking does not reach the desired value.

Also known in the art is a zirconium leather tanning agent which, whencompared to the titanium tanning agent, increases the temperature oftanned pelt shrinking (cf. A. I. Metelkin, N. I. Kolesnikova, E. V.Kuz'mina "Zirconium Tanning", 1972, "Legkaya Industriya" (LightIndustry) Publishing House, Moscow, p. 220). However, the zirconiumtanning agent is more expensive than the titanium tanning agent.

A tanning agent is also known, which contains both titanium andzirconium, the application of which results in an improved quality ofleather (cf. USSR Inventor's Certificate No. 340702, Cl. 28a, 1972).

The process for the manufacture of this tanning agent comprises thesteps of mixing two solutions: a solution containing a salt of titaniumand a solution containing a salt of zirconium, whereafter the solutionsare evaporated to dryness. This process involves increased power input.

SUBJECT OF THE INVENTION

The present invention is directed to a leather tanning agent that issuperior to the prior art tanning agents (including titanium) in itsproperties and could be produced by a simple process using readilyavailable reagents and mineral stock materials.

The objective of the invention is accomplished by providing a leathertanning agent incorporating sulphate of titanyl and ammonium, which,according to the present invention, contains the following components,in percent by weight:

    ______________________________________                                        sulphate of aluminum and ammonium                                                                      3 to 20                                              containing 0.001 to 1.0% of TiO.sub.2 or                                      TiO.sub.2 and ZrO.sub.2                                                       and/or sulphate of zirconium and ammonium                                                             20 to 50                                              containing 0.001 to 0.5% of TiO.sub.2                                         or TiO.sub.2 and Al.sub.2 O.sub.3                                             and sulphate of titanyl and ammonium                                          containing of 0.001 to 1.0% of Al.sub.2 O.sub.3                               and/or ZrO.sub.2        the balance.                                          ______________________________________                                    

The above-stated additives of TiO₂, ZrO₂ and Al₂ O₃ incorporated in theabove-specified sulphates are present therein in a chemically combinedstate.

The tanning agent of such composition has the advantage that it enableseffective tanning of hides so as to impart excellent physico-mechanicalcharacteristics thereto.

The term "sulphate of ammonium and aluminum" is used here to denote acompound of the formula NH₄ AL(SO₄)₂.12H₂ O, which contains chemicallycombined additives of TiO₂ or TiO₂ and ZrO₂.

The term "sulphate of zirconium and ammonium" is used here to denote acompound of the formula (NH₄)₂ Zr₂ (OH)₅.(SO₄)₂,5.H₂ O, which containschemically combined additives of TiO₂ or TiO₂ and Al₂ O₃.

The term "sulphate of titanyl and ammonium" is used to denote a compoundof the formula (NH₄)₂ TiO(SO₄)₂.H₂ O, which contains chemically combinedadditives of Al₂ O₃ and/or ZrO₂.

The tanning agent of the present invention is produced by a processwhich, according to the present invention, comprises reacting a solutioncontaining 80 to 200 g/l of titanium as calculated for titanium dioxidewith a solution of aluminum sulphate containing 80 to 130 g/l ofaluminum as calculated for aluminum oxide, and/or a solution ofzirconium sulphate containing 50 to 200 g/l of zirconium as calculatedfor zirconium oxide in the presence of sulphuric acid and ammoniumsulphate.

The process for producing the tanning agent according to the presentinvention is advantageous in that it can be readily realized on acommercial scale, since the process is carried out under ambientconditions: at room temperature and ambient pressure with the use ofreadily available and inexpensive reagents and mineral raw materials.

PREFERRED EMBODIMENTS OF THE INVENTION

The following embodiments of the composition of the sulphate tanningagent are covered by the present invention, depending on the combinationof the sulphates employed, namely, 2-component and 3-component tanningagents.

A titanium-aluminum tanning agent has the following composition, percentby weight:

    ______________________________________                                        sulphate of aluminum and ammonium con-                                                                 3 to 20                                              taining 0.001 to 1.0% of TiO.sub.2                                            sulphate of titanyl and ammonium contain-                                                              the balance.                                         ing 0.001 to 1.0% of Al.sub.2 O.sub.3                                         ______________________________________                                    

This tanning agent makes it possible to increase the temperature oftanned pelt shrinking by 4°-6° C. as compared to the prior art titaniumtanning agent.

A titanium-zirconium tanning agent has the following composition,percent by weight:

    ______________________________________                                        sulphate of zirconium and ammonium con-                                                                20 to 50                                             taining 0.001 to 0.1% of TiO.sub.2                                            sulphate of titanyl and ammonium contain-                                                              the balance.                                         ing 0.001 to 0.1% of ZrO.sub.2                                                ______________________________________                                    

This tanning agent makes it possible to increase the shrinkingtemperature of pelt tanned therewith by 8°-9° C. as compared to theprior art titanium tanning agent.

A titanium-zirconium-aluminum tanning agent has the followingcomposition percent by weight:

    ______________________________________                                        sulphate of aluminum and ammonium con-                                                                  3 to 20                                             taining 0.001 to 1.0% of TiO.sub.2 and ZrO.sub.2                              sulphate of zirconium and ammonium contain-                                                            20 to 50                                             ing 0.001 to 0.5% of TiO.sub.2 and Al.sub.2 O.sub.3                           sulphate of titanyl and ammonium containing                                                            the balance.                                         0.001 to 1.0% of Al.sub.2 O.sub.3 and ZrO.sub.2                               ______________________________________                                    

This tanning agent makes it possible to increase the shrinkingtemperature of pelt tanned therewith by 10°-12° C. as compared to theprior art titanium tanning agent.

The titanium-aluminum tanning agent according to the present inventioncan also include 1 to 10% by weight of silicic acid which serves as afiller for leather and makes it possible to increase its yield by weightand thickness after tanning by 0.8 to 1.0% as compared to the prior arttitanium tanning agent.

The choice of the content ranges of the above-specified sulphates in thetanning agent according to the present invention is dictated by theamount of the sulphates of aluminum and ammonium. Thus, if the sulfatesof aluminum and ammonium are less than 3% by weight, no activation ofthe tanning effect of titanyl and ammonium sulphate is displayed by thetanning agent. An increase in the amount of sulphates of aluminum andammonium above 20% by weight causes a reduction of the amount of themain tanning component, i.e. of sulphate of titanyl and ammonium, whichresults in a reduction of the tanning properties.

Where the amount of the sulphates of zirconium and ammonium in thetanning agent is less than 20% by weight, its tanning effect isweakened, whereas, with the amount of this component exceeding 50% byweight, the tanning effect of titanium is suppressed by zirconium and,moreover, this adds to the cost of the tanning agent.

The choice of concentration ranges of additives of TiO₂, ZrO₂ and Al₂ O₃chemically combined in sulphates is dictated by the fact that below0.001% by weight they do not display the effect of activation ofsulphates in tanning, whereas the upper limit of the range is defined bythe conditions of the process for the production of the tanning agent.

The following embodiments of the process for producing the tanning agentaccording to the present invention are possible depending on thecharacter of the tanning agent to be produced: titanium-aluminum, ortitanium-zirconium, or titanium-zirconium-aluminum.

According to the present invention, the titanium-aluminum tanning agentis produced by a process wherein a solution of sulphate of titanyl andammonium containing 80 to 140 g/l of titanium, as calculated fortitania, is added to ammonium sulphate and sulphuric acid untilcrystallization of the sulphates of titanyl and ammonium begins.Thereafter a solution of aluminum sulphate and additionally ammoniumsulphate and sulphuric acid are added during a period of from 1 to 5hours until the total content of free sulphuric acid and aluminumsulphate in the reaction solution becomes equal to 400-600 g/l and themolar ratio of aluminum to titanium is equal to 0.03-0.24:1.

The titanium-aluminum tanning agent can also be produced from asulphuric acid solution containing 100 to 200 g/l of titanium ascalculated for titania and 300 to 520 g/l of sulphuric acid, thissolution resulting from processing of titanium-containing stockmaterials. Ammonium sulphate is added to this solution, until theresulting sulphate of titanyl and ammonium begins to crystallize,whereafter a solution of aluminum sulphate and additionally ammoniumsulphate are added until the content of free ammonium sulphate in thereaction solution becomes 210 to 350 g/l and the molar ratio ofaluminum-to-titanium is 0.03-0.24:1.

The use of the above-mentioned sulphuric acid solution has the followingadvantages: (1) there is no need in special recovery of titanyl andammonium sulphate therefrom; (2) the degree of precipitation of titaniumfrom this sulphate solution is higher than from the solution of sulphateof titanyl and ammonium, and (3) the resulting product has bettertanning properties.

To enhance tanning characteristics of the titanium-aluminum tanningagent, the process for producing it is conducted with the addition of 1to 10% by weight of silicic acid or its sodium salt. Silicic acidincorporated in the tanning agent composition serves as a filler andincreases the yield of leather both in weight and thickness.

According to the present invention, the process for producing atitanium-zirconium tanning agent comprises introduction into azirconium-containing solution of ammonium sulphate and sulphuric aciduntil the beginning of crystallization of the forming sulphate ofzirconium and ammonium, whereafter during a period of from 1 to 5 hoursa solution of sulphate of titanyl and ammonium is added containing 80 to140 g/l of titanium as calculated for titania, and additionally ammoniumsulphate and sulphuric acid is also introduced until the total contentof free ammonium sulphate and sulphuric acid in the reaction solutionbecomes equal to 770-1,000 g/l and the molar ratio of zirconium totitanium is equal to 0.10-0.65:1.

Described hereinbelow are two embodiments of the process for producing atitanium-zirconium-aluminum tanning agent. In one embodiment azirconium-containing solution is added to ammonium sulphate andsulphuric acid until the moment of crystallization of the resultingsulphate of zirconium and ammonium. Thereafter during a period of from 1to 5 hours it is added to a solution of ammonium titanyl containing 80to 140 g/l of titanium as calculated for titania, a solution of aluminumsulphate, and additionally with ammonium sulphate and sulphuric aciduntil the total content of free ammonium sulphate and sulphuric acid inthe reaction solution becomes equal to 770-1,000 g/l and the molar ratioof aluminum and zirconium to titanium is equal to 0.03-0.24:0.10-0.65:1.

Another embodiment of the process for producing thetitanium-zirconium-aluminum tanning agent comprises addition into azirconium-containing solution of a sulphuric acid solution containing100 to 200 g/l of titanium based on titania and 300 to 520 g/l ofsulphuric acid obtained from processing a titanium-containing rawmaterial for a period of from 6 to 10 hours, along with a solution ofaluminum sulphate and ammonium sulphate till the content of freeammonium sulphate in the reaction solution is 400 to 580 g/l and themolar ratio of aluminum and zirconium to titanium is equal to0.03-0.24:1.10-0.65:1.

In all the embodiments the process for producing a sulphate tanningagent is effected at room temperature under normal pressure. Thestarting raw materials and reagents are readily available materials.

For the preparation of a titanium-containing solution use is made eitherof sulphate of titanyl and ammonium obtained from processing atitanium-containing raw material, or of this raw material aftertreatment thereof with sulphuric acid. As said raw material use can bemade of ilmenite concentrate, sphene concentrate, leucoxene concentrate,and other concentrates of titanium materials.

For the preparation of a zirconium-containing solution use is made ofzirconium sulphate obtained from processing a zirconium containing rawmaterial, for example, zircon concentrate.

For a better understanding of the present invention some specificexamples illustrating the production of the tanning agent are givenhereinbelow.

EXAMPLE 1

500 g of sulphate of titanyl and ammonium are dissolved in 1 liter ofwater to obtain a solution containing 100 g/l of titanium as calculatedfor its dioxide.

Into the resulting solution ammonium sulphate and sulphuric acid areadded until the beginning of crystallization of sulphate of titanyl andammonium, whereafter during 2 hours there is added 0.04 l of thesolution of aluminum sulphate containing 113 g/l of aluminum ascalculated for its oxide and additionally aluminum sulphate andsulphuric acid until the total content of free sulphuric acid andammonium sulphate in the reaction solution is 550 g/l and the molarratio of aluminum to titanium is equal to 0.05-1. The resultingprecipitate is separated from the solution by filtration.

The final product yield is 540 g. It contains, percent by weight: TiO₂,18.2; Al₂ O₃, 1.2. It consists of two sulphates, percent by weight:

    ______________________________________                                        sulphate of aluminum and ammonium                                                                     13                                                    containing 0.5% of TiO.sub.2                                                  sulphate of titanyl and ammonium                                                                      the balance.                                          containing 0.5% of Al.sub.2 O.sub.3                                           ______________________________________                                    

EXAMPLE 2

Use is made of 1 liter of a sulphuric acid solution obtained fromprocessing a titanium-containing stock containing 160 g/l of titanium ascalculated for its dioxide and 400 g/l of sulphuric acid. Into thissolution ammonium sulphate is added till the beginning ofcrystallization of the forming sulphate of titanyl and ammonium,whereafter during 8 hours it is added to 0.2 l of a solution of aluminumsulphate containing 113 g/l of aluminum as calculated for alumina, andadditionally ammonium sulphate until the content of free ammoniumsulphate in the solution becomes equal to 300 g/l and the molar ratio ofaluminum to titanium is 0.20:1. The precipitate is separated from thesolution by filtration.

The yield of the final product is 980 g. It contains, percent by weight:TiO₂, 16.3; Al₂ O₃, 2.05. It consists of two sulphates, percent byweight:

    ______________________________________                                        sulphate of aluminum and ammonium                                                                     17.8                                                  containing 0.6% TiO.sub.2                                                     sulphate of titanyl and ammonium                                                                      the balance.                                          containing 0.6% of Al.sub.2 O.sub.3                                           ______________________________________                                    

EXAMPLE 3

The process is conducted as described in the foregoing Examples 1 and 2,except that after the introduction of the components, silicic acid isadded in an amount of 3.8 g (in the experiment of Example 1) and 6.0 g(in the experiment of Example 2).

In the final product the weight ratio of silicic acid to titaniumdioxide is 0.05:1.

EXAMPLE 4

0.5 liters of a solution of zirconium sulphate containing 180 g/l ofzirconium as calculated for its dioxide is added to sulphuric acid andammonium sulphate until the total content of free sulphuric acid andammonium sulphate becomes equal to 770 g/l. This results incrystallization of the formed sulphate of zirconium and ammonium fromthe solution. Into the reaction solution during two hours there is added1 liter of a solution of sulphate of titanyl and ammonium containing 117g/l of titanium as calculated for its dioxide, and additionally ammoniumsulphate and sulphuric acid to a total content of free sulphuric acidand ammonium sulphate of 820 g/l and the molar ratio of zirconium totitanium of 0.5:1. The suspension is allowed to stand for 24 hours. Theprecipitate is separated by filtration.

The product yield is 1,000 g. It contains, percent by weight: TiO₂,11.0; ZrO₂, 8.5 The product consists of two sulphates, percent byweight:

    ______________________________________                                        sulphate of zirconium and ammonium                                                                    45                                                    containing 0.005% of TiO.sub.2                                                sulphate of titanyl and ammonium                                                                      the balance.                                          containing 0.005% of ZrO.sub.2                                                ______________________________________                                    

EXAMPLE 5

Use is made of 0.5 liters of a solution of zirconium containing 180 g/lof zirconium as calculated for its dioxide. During 8 hours the solutionis added to 1 liter of a sulphuric acid solution obtained fromprocessing a titanium-containing raw material containing 160 g/l oftitanium as calculated for its dioxide and 400 g/l of sulphuric acid, aswell as ammonium sulphate until the content of free ammonium sulphate inthe solution is 500 g/l and the molar ratio of zirconium to titanium is0.35:1. The suspension is allowed to stand for 35 hours. The precipitateis separated by filtration.

The yield of the final product is 1,200 g. It contains, percent byweight: TiO₂, 12.9; ZrO₂, 7.3. The product consists of two sulphates,percent by weight: sulphate of zirconium and ammonium containing 0.006%of TiO₂ 35 sulphate of titanyl and ammonium containing 0.006% of ZrO₂the balance.

EXAMPLE 6

Use is made of 0.5 liters of a solution of zirconium sulphate containing180 g/l of zirconium as calculated for zirconia. Sulphuric acid andammonium sulphate are added to this solution until the total content offree ammonium sulphate and sulphuric acid becomes equal to 770 g/l. Theformed sulphate of ammonium and zirconium starts to crystallize out ofthe solution. Into the reaction solution there are added during 1 hour1.5 liters of a solution of sulphate of titanyl and ammonium containing100 g/l of titanium as calculated for titania, 0.05 liters of a solutionof aluminum sulphate containing 113 g/l of aluminum as calculated foralumina, and additionally sulphuric acid and ammonium sulphate till thetotal content of free sulphuric acid and ammonium sulphate in thesolution is 820 g/l and the molar ratio of aluminum and zirconium totitanium is made equal to 0.05:0.40:1. The suspension is allowed tostand for 20 hours. The precipitate is separated by filtration.

The yield of the final product is 1,500 g. It contains, percent byweight: TiO₂, 9.5; ZrO₂, 5.9; Al₂ O₃, 0.3.

The product consists of three sulphates, percent by weight:

    ______________________________________                                        sulphate of aluminum and ammonium                                                                      3                                                    containing 0.5% of TiO.sub.2 and ZrO.sub.2                                    sulphate of zirconium and ammonium                                                                    45                                                    containing 0.2% of TiO.sub.2, and Al.sub.2 O.sub.3                            sulphate of titanyl and ammonium                                                                      the balance.                                          containing 0.4% of Al.sub.2 O.sub.3 and ZrO.sub.2                             ______________________________________                                    

EXAMPLE 7

Use is made of 0.5 liters of a solution of zirconium sulphate containing150 g/l of zirconium as calculated for its dioxide. Into this solutionthere are added during 8 hours, 1.7 liters of a sulphate solutionobtained from processing of a titanium-containing raw materialcontaining 160 g/l of titanium as calculated for its dioxide and 400 g/lof sulphuric acid, 0.04 liters of a solution of aluminum sulphatecontaining 113 g/l of aluminum as calculated for its oxide, and ammoniumsulphate until the content of free ammonium sulphate in the reactionsolution is 500 g/l and the molar ratio of aluminum and zirconium totitanium is 0.18:0.20:1. The suspension after the addition of thereagents, is allowed to stand for 40 hours. The precipitate is separatedby filtration.

The weight of the precipitate is 1,885 g. It contains, percent byweight: TiO₂, 14.0; ZrO₂, 4.3; Al₂ O₃, 2.8. The product consists ofthree sulphates, percent by weight:

    ______________________________________                                        sulphate of aluminum and ammonium                                                                     20                                                    containing 0.5% of TiO.sub.2 and ZrO.sub.2                                    sulphate of zirconium and ammonium                                                                    21                                                    containing 0.2% of TiO.sub.2 and Al.sub.2 O.sub.3                             sulphate of titanyl and ammonium                                                                      the balance.                                          containing 0.6% of Al.sub.2 O.sub.3 and ZrO.sub.2                             ______________________________________                                    

The process according to Examples 1 through 7 is performed under normalconditions, i.e. at room temperature and normal pressure.

Tanning properties of the products according to the shrinkingtemperature of the pelt treated therewith (are given in the tablehereinbelow).

                  TABLE                                                           ______________________________________                                        Tanning properties of the products                                                                    Temperature                                                                   of tanned                                             Tanning agent           pelt shrinking, °C.                            1                       2                                                     ______________________________________                                        Sulphate of titanyl and ammonium                                                                      85                                                    (prior art titanium tanning agent)                                            Titanium-aluminum tanning agent                                                                       89                                                    according to Example 1                                                        Titanium-aluminum tanning agent                                                                       91                                                    according to Example 2                                                        Titanium-aluminum-silicon tanning                                                                     92                                                    agent according to Example 3                                                  Titanium-zirconium tanning agent                                                                      93                                                    according to Example 4                                                        Titanium-zirconium tanning agent                                                                      94                                                    according to Example 5                                                        Titanium-zirconium-aluminum tanning                                                                   95                                                    agent according to Example 6                                                  Titanium-zirconium-aluminum tanning agent                                                             97                                                    according to Example 7                                                        ______________________________________                                    

From the data showing the shrinking temperature of pelt tanned with theabove-specified tanning agents it follows that the tanning agentaccording to the present invention produced as described in Examples 1through 7 improves the quality of leather as compared to the prior arttitanium tanning agent.

The best characteristics as regards the temperature of tanned peltshrinking are attained in the case of the titanium-zirconium-aluminumtanning agent produced with the use of a sulphate solution resultingfrom processing a titanium-containing raw material (Example 7).

Enhanced tanning characteristics of the tanning agent of the presentinvention as compared to those of the prior art tanning agents are dueto the use of a combination of sulphates incorporating, as it has beenalready specified hereinbefore, additives of TiO₂, ZrO₂ and Al₁ O₃.

INDUSTRIAL APPLICABILITY

The present invention can be used in the leather industry for leatherprocessing.

What we claim is:
 1. A process for producing a leather tanning agent,comprising reacting (a) solution containing 80 to 200 g/l of titanium,as calculated for its dioxide, with (b) a solution of aluminum sulphatecontaining from 80 to 130 g/l of aluminum, as calculated for its oxide,and (c) a solution of zirconium sulphate containing 50 to 200 g/l ofzirconium, as calculated for its dioxide, in the presence of sulphuricacid and ammonium sulphate.
 2. The process of claim 1, wherein thetitanium solution (a) is sulphate of titanyl and ammonium containingfrom 80 to 140 g/l of titanium, as calculated for its dioxide, which isadded to ammonium sulphate and sulphuric acid until crystallization ofthe sulphate of titanyl and ammonium begins, thereafter adding asolution of sulphate of ammonium and sulphuric acid for 1 to 5 hours, toobtain a total content of free sulphuric acid and ammonium sulphate of400 to 600 g/l, and a molar ratio of aluminum to titanium of0.03-0.24:1.
 3. The process according to claim 1, wherein said solution(a) is a sulphate solution obtained from processing a titanium rawmaterial containing 100 to 200 g/l of titanium, as calculated for itsdioxide, and 300 to 520 g/l of sulphuric acid; this titanium sulphatesolution being added to ammonium sulphate until crystallization of theformed sulphate of titanyl and ammonium begins, thereafter adding asolution of aluminum sulphate along with an additional amount ofammonium sulphate for a period of from 6 to 10 hours to obtain a freeammonium sulphate content in the reaction solution of 210 to 350 g/l anda molar ratio of aluminum to titanium of 0.03-0.24:1.
 4. A processaccording to claim 3, wherein silicic acid or its sodium salt is addedto obtain a molar ratio of silicon to titanium of 0.07-0.70:1.
 5. Theprocess of claim 1, wherein ammonium sulphate and sulphuric acid areadded to said zirconium sulphate solution until crystallization of theformed sulphate of zirconium and ammonium begins, thereafter adding asolution of sulphate of titanyl and ammonium containing 80 to 140 g/l oftitanium, as calculated for its dioxide, for 1 to 5 hours, and addingammonium sulphate and sulphuric acid until obtaining a total content offree ammonium sulphate and sulphuric acid in the reaction solution offrom 770 to 1,000 g/l and a molar ratio of zirconium to titanium of0.10-0.65:1.
 6. The process of claim 5, wherein after thecrystallization of the sulphate of ammonium and zirconium begins, asolution of aluminum sulphate is added thereto until obtaining a molarratio of aluminum and zirconium to titanium in the solution equal to0.03-0.24:0.10-0.65:1, respectively.
 7. The process according to claim1, wherein a sulphate solution is added to the zirconium solution (c)for a period of from 6 to 10 hours; said sulphate solution obtained fromthe processing of a titanium raw material containing 100 to 200 g/l oftitanium, as calculated for its dioxide, and 300 to 520 g/l of sulphuricacid and ammonium sulphate, until obtaining a content of free ammoniumsulphate in the reaction solution of from 400 to 580 g/l and a molarratio of zirconium to titanium of 0.10-0.65:1.
 8. The process of claim7, wherein a solution of aluminum sulphate is added to the reactionsolution to obtain a molar ratio of aluminum and zirconium to titaniumin the solution of 0.03-0.24:0.10-0.65:1, respectively.
 9. A leathertanning agent with components selected from the group consisting of:(a)3 to 20% sulphate of aluminum and ammonium, containing 0.001 to 1.0% ofTiO₂, or TiO₂ and ZrO₂, (b) 20 to 50% sulphate of zirconium andammonium, containing 0.001 to 0.5% of TiO₂ or TiO₂ and Al₂ O₃, and (c)mixtures of (a) and (b); the balance of said leather tanning agentcomprising sulphate of titanyl and ammonium containing 0.001 to 1.0% ofAl₂ O₃ or Al₂ O₃ and ZrO₂.
 10. The tanning agent of claim 9, comprising,in % by weight:3 to 20% sulphate of aluminum and ammonium containing0.001 to 1.0% of TiO₂, and the balance comprising sulphate of titanyland ammonium containing 0.001 to 1.0% of Al₂ O₃.
 11. The tanning agentof claim 10, also containing 1 to 10% by weight of silicic acid.
 12. Thetanning agent of claim 9, comprising, in % by weight:20 to 50% sulphateof zirconium and ammonium containing 0.001 to 1.0% of TiO₂, the balancecomprising sulphate of titanyl and ammonium containing 0.001 to 1.0% ofCrO₂.
 13. The tanning agent of claim 9, comprising, in % by weight:3 to20% sulphate of aluminum and ammonium containing 0.001 to 1.0% of TiO₂and ZrO₂, 20 to 50% sulphate of zirconium and ammonium containing 0.001to 0.5% of TiO₂ and Al₂ O₃, and the balance comprising sulphate oftitanyl and ammonium containing 0.001 to 1.0% of Al₂ O₃ and ZrO₂. 14.The tanning agent of claim 9, wherein TiO₂, ZrO₂ and Al₂ O₃ contained inthe sulphates are present in a chemically combined state.
 15. A processfor producing a leather tanning agent, comprising the steps of:(a)reacting a solution containing 80-200 g/l of titanium as calculated forits dioxide, with ammonium sulphate and sulphuric acid until the startof crystallization of sulphate of titanyl and ammonium; (b) adding tothe mixture of step (a), a solution selected from the group consistingof:(i) an aluminum sulphate solution containing 80-130 g/l of aluminumas calculated for its oxide, (ii) a zirconium sulphate solutioncontaining 50-200 g/l of zirconium as calculated for its dioxide, (iii)and mixtures thereof; (c) further adding sulphuric acid and ammoniumsulphate for a period of 1 to 5 hours until the reacting solution has atotal content of free sulphuric acid and ammonium sulphate, of 400-600g/l, and the aluminum to titanium molar ratio is 0.03-0.24:1,respectively; (d) separating the resulting sediment from the solution.